CROI 2021: HIV capsid uncoats in the CD4 nucleus rather than the cytoplasm – viral lifecycle updated…

Simon Collins, HIV i-Base

In the first plenary lecture at CROI 2021, Hans-Georg Kräusslich prevented evidence showing that HIV capsid remains intact until entering the CD4 cell nucleus. [1]

This has been an ongoing debate for many years that i-Base has reported before, including at previous CROI. [2, 3]

The talk included incredible animations using electromicrosopy for both SARS-CoV-2 and HIV.

Researchers at CROI 2021 showed that capsid uncoats in the nucleus. This overturns decades of belief that reverse transcriptase converts HIV RNA to DNA in the cytoplasm.

In the HIV studies, radio-labelled proteins showed the capsid journey in real-time, to slip through pores in the nuclear core complex, narrow end first, with nanometres to spare. These images are able to show the empty capsid still intact within the nucleus (from 24.30 in the webcast).


The accumulating studies showing capsid uncoating as a late-stage event seem to be convincing a wider consensus among researchers.

This seemed a good time to update community diagrams on the viral lifecycle – and the most used versions are now updated on the i-Base website. [4–7]

Maybe for a few medical textbooks too?


  1. Kräusslich H-G. Imaging viral lifecycles. Plenary talk. CROI 2021. (abstract) (webcast)
  2. New online animation of HIV lifecycle. HTB (May 2018)
  3. Iwasa J. Seeing HIV: animating the HIV lifecycle. Program committee workshop for new investigators and trainees. CROI 2018 Abstract 14. (webcast)
  4. HIV i-Base, The viral lifecycle – updated diagram.
  5. HIV i-Base. The viral lifecycle. ART in Pictures (2019)
  6. HIV i-Base. The viral lifecycle in detail. ART in Pictures (2019)
  7. HIV i-Base. HIV life cycle – how drugs work in different ways. Introduction to ART.

This report was first posted on 9 March 2021.

Links to other websites are current at date of posting but not maintained.